This invention relates to a dynamic photoelasticimeter employing a rotating birefringent element.
Static photoelasticimeters which comprise rotating birefringent plates are described in copending U.S. patent application Ser. No. 835,004 filed Sept. 20, 1977. While the devices described in the aforesaid application permit study of a static model, the optical and electronic arrangements do not make it possible to carry out in a simple manner measurements in dynamic photoelasticimetry; that is, when the model to be studied is excited by shocks or by periodic vibrations.
The characteristic parameters at a given point of a birefringent model to be studied are the orientation .theta. of the fast axis of the point and the phase shift .phi. produced by the model between the light vectors moving along the fast axis and along the slow axis at the point. In the event the model to be studied is subjected to impacts or vibrations, these parameters .theta. and .phi. are functions of time.
In the following description, the letter .omega. is used either to designate frequencies or angular frequencies. The expression "birefringent" is used as a noun to designate an element which possesses birefringence (double refraction); for instance, a "rotating birefringent" may designate a mechanically turning doubly refracting plate or a Kerr cell subjected to a rotating field or the like.